PULSE WIDTH MODULATION (PWM) Using 555 Timer IC

What is modulation?

In analog or digital communication system, it is impossible to transmit a low frequency message signal over a channel, it causes signal distortion, attenuation or signal loss. Inorder to make the transmission ideal (almost), we have to use some techniques called modulation. Modulation can be defined as the process of varying some characteristics of carrier signal in accordance with the instantaneous value of message signal. Carrier signal is a high frequency wave generated by a local oscillator, used to carry the message signal from transmitter to reciever. The message signal which is mixed with carrier wave is called modulated signal and the process is called Modulation. The modulation is an important process in a basic communication system, which increases the transmission range, reduces the size of antenna and increases the efficiency of the system by reducing noise interference.

What is pulse width modulation (PWM)? How it is generated using 555 timer IC?

Pulse width modulation is a process of varying the width of carrier signal according to the instantaneous amplitude value of message signal. PWM is also known as Pulse Duration Modulation (PDM) or Pulse Length Modulation (PLM). It utilises the advantages of constant amplitude pulses.

CIRCUIT DIAGRAM OF PWM USING 555 TIMER

INPUT AND OUTPUT WAVEFORMS OF PWM

In the circuit diagram, the 555 IC is wired as monostable multivibrator, which varies the output period of oscillations according to the amplitude of message signal. That is, Trigger is applied to control the starting time of pulses and modulating signal is fed to control the duration of pulses.